Working overseas is tricky if your visa is sponsored by an employer.
I will show you some other ways to make money to decrease your risk of immigration problems.
Technically, you can NOT have any additional work without written consent from your "visa sponsor". This is written into most contracts and a breach of contract could be grounds for employment termination.
This means that picking up side English teaching jobs or freelancing can put you at risk of being fined and possibly deported. If you want to teach additional side jobs, do so at your own risk and always get cash.
Occasionally, there will be people who will turn you into immigration. So I would not suggest doing this.
Get paid to your USA/home bank account or US
There will be no record of you receiving payment here in Korea.
Below are some ways most teachers earn extra cash online now.
#1 - Online teaching - Sites like VipKid and Italki are very popular these days. The main requirements here are that you have a stable internet connection. You don't want to waste time teaching a lesson and not get paid if your internet cuts out. There are dozens of companies out there but these seem to be the largest at this time.
#2 - Become a Tour Guide - Sites like Verramente allow you to create your own tours on your own schedule. If you love showing people around the city, this won't even feel like work. Meet new people and show them the hidden gems of your town.
#3 - Creating a WordPress travel blog - If you love taking pictures and sharing your travel and tips, this is a great hobby. Many earn money through AdWords or other paid advertising. There have been some amazing blogs that have come out of teaching here for only a few years. Let everyone know your tips, every experience is a different story.
These three options above allow you to receive payments to your US or home bank account. That is the best way to avoid any immigration issues. You can simply withdraw money from an ATM and the currency conversion will be done by your bank.
Please share and add comments below on any suggestions you have.
Thank you :)